1. Field of the Invention
The present invention relates to a method for indicating slower than acceptable system response in an on-board central tire inflation system of the type having a plurality of selectable operating settings (i.e. levels) of the inflation pressurization.
2. Description of the Prior Art
On-board central tire inflation systems (CTIS), also known as tire traction systems, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,102,573; 3,276,502; 3,276,503; 4,313,483; 4,418,737; 4,421,151; 4,434,833; 4,640,331 and 4,678,017, the disclosures of all of which are hereby incorporated by reference. CTIS allow the operator to remotely manually and/or automatically vary and/or maintain the inflation pressure of one or more of the vehicle tires from the vehicle (usually a truck) air system, usually while the vehicle is in motion as well as when the vehicle is at rest.
It is well known that the traction of vehicles on relatively soft terrain (i.e. on mud, sand or snow) may be greatly improved by decreasing the inflation pressure within the tires. By decreasing the inflation pressure, the tire supporting surface (usually called the "footprint") will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desirable to decrease the tire pressure from the over-the-road or highway inflation pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth roads thereby increasing economy and safety. Accordingly, in cross country vehicles it is desirable to change the inflation pressure in the pneumatic tires to fit the terrain and is also desirable that a system be provided for changing the inflation pressure of the tires from an on-board source, while the vehicle is at motion or at rest and that the system be controlled from the vehicles operating cab.
In a particular type of CTIS, as illustrated and described in above-mentioned U.S. Pat. No. 4,640,331, a plurality of wheel ends (each comprising one or more tires) are each fluidly connected by a separate branch conduit to common central conduit which may be connected to a source of pressurized air for inflating the tires, to a source of regulated pressurized air for deflating the tires and/or, to atmosphere for venting the conduits and relieving pressure across the rotating seals. The common conduit and/or a measurement conduit may also be pressurized by means of a quick release valve or the like to the average pressure of the various branch conduits. A single pressure transducer is provided in fluid communication with the measurement conduit and/or the common central conduit, remote from the wheel ends, for sensing a value indicative of the pressure or average pressure in the inflatable tires.
While the on-board CTIS described above is highly advantageous as pressure venting is remote from the wheel ends and a single pressure transducer, located in a relatively well protected location remote from the wheel ends and/or the vehicle under carriage, can be utilized to sense tire inflation of the vehicle tires or groups of tires, the CTIS was not totally satisfactory in that excessive times for inflation or deflation were not recognized, thereby causing prolonged system operation when further change of tire pressure was not occurring.